1. Field of the Invention
This invention relates to a method of dressing, dressing system and dressing electrode for a conductive grindstone, particular for a conductive grindstone using super abrasive grains such as diamonds, CBN and the like, and more particularly to the method of performing dressing and trueing processes for the above mentioned grindstone and dressing system and the novel dressing electrode for carrying out this method.
2. Prior Art
Dressing and trueing for a normal grindstone using green-carborundom, alundom and the like as abrasive grains is generally carried out as follows. First, the grindstone is formed to be a discshape and rotated. Then, a diamond dresser using one or many diamond abrasive grains is pressed against the ground surface of the grindstone. Simultaneously, either the grindstone or the dresser is reciprocated in a direction being parallel to the rotating shaft of the disc.
However, it is impossible or extremely difficult to perform the dressing process for a grindstone using super abrasive grains such as diamond, CBN and the like with the above mentioned method' because, the super abrasive grains of the grindstone are much harder than the green-carborundom, alundom. Additionally, the diamond used as super abrasive grains is often worn out due to the heat generated during the dressing process.
Therefore, the grindstone is ground with a steel, which is not quenched to be so-called raw material, for long time. A brake dresser also can be used while it is rotating during the dressing process. These methods can be used effectively for resin bond or glass bond grindstones using super abrasive grains to some degree. However, with these methods, it takes an extremely long time to perform the dressing process particularly the trueing process for the metal bond grindstones using super abrasive grains where the super abrasive grains are bonded surely, thus, these methods can not be utilized at all for the above mentioned grindstones.
Lately, an electrolytic dressing method of the dressing and trueing processes for the metal bond grindstones using super abrasive grains has become practical.
This dressing method is performed for the metal bond grindstone which is used in a cutting or grinding process. First, a dressing electrode formed of black lead, rustless steel, copper alloy and the like is disposed adjacent the peripheral face (ground surface) of the grindstone so that there is a predetermined gap between the electrode and the grindstone. Then, while a conductive processing fluid is supplied to the gap, a voltage is applied between the electrode and the grindstone so as to provide a positive pole on the grindstone. Shavings and/or bond metal of the grindstone, which are attached to the surface of the grindstone during the cutting or grinding process, are melted with electrolytic action. Thus, the metal bond grindstone can be ground. However, in this electrolytic dressing method, there are various problems as follows.
1. During the dressing process for the ground surface of the grindstone, the distance of the gap between the dressing electrode and the grindstone becomes inconsistent due to the difference of the ejected length of the abrasive grains from the ground surface of the grindstone and the difference of the amount of accumulated shavings and the like on this surface. Then, the electrolytic action can not be applied to the whole of this surface uniformly. Therefore, this surface facing the dressing electrode is deformed asymmetrically with respect to the center line of this surface. That is to say, "geometric distortion" is caused on this surface. If the grindstone is used for cutting a workpiece, the grindstone is often deformed during the cutting process due to this "geometric distortion", whereby the workpiece can not be cut straightly. Additionally, the grindstone is bent backward due to this "geometric distortion", which is a critical defect for the cutting grindstone. As a result, it is impossible to precisely cut workpieces. When a grindstone is used for grinding a workpiece, the grindstone generally has a width (thickness) in the direction parallel to the rotating shaft of the grindstone. In this case, due to this "geometric distortion", the ground surface can not remain smooth during the grinding process. As a result, it is impossible to grind the workpiece precisely with the conventional electrolytic dressing method.
2. In the trueing process for the grindstone, the ground surface of the grindstone should be shaved enough so that a considerably large amount of shavings are removed. In this conventional electrolytic dressing method, during the dressing process for the grindstone, an insulating layer preventing the electrolytic action is produced on the ground surface. Thus, the voltage for the dressing process is decreased. Consequently, corresponding to the decreasing of the dressing voltage, the trueing speed gradually approaches zero. Finally, the trueing process is substantially stopped. Although all of the bond metal and shavings must be melted by this action for finishing the dressing process, the abrasive grains can not be removed completely from the grindstone since this method is progressed only by this electrolytic action. Therefore, even if long time is taken, the trueing process can not be performed substantially with the conventional electrolytic dressing method.